Data decompression using a construction area

ABSTRACT

For serving sequential read patterns from a compressed journal storage system, a construction area cache algorithm is used to temporarily store the read and decompressed data in a user view sequential order to minimize disk I/Os and CPU utilization while serving the data to the user.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to computers, and moreparticularly, to data decompression using a construction area.

2. Description of the Related Art

In today's society, computer systems are commonplace. Computer systemsmay be found in the workplace, at home, or at school. Computer systemsmay include data storage systems, or disk storage systems, to processand store data. Data storage systems, or disk storage systems, areutilized to process and store data. A storage system may include one ormore disk drives. These data processing systems typically require alarge amount of data storage. Customer data, or data generated by userswithin the data processing system, occupies a great portion of this datastorage. Many of these computer systems include virtual storagecomponents. Data compression is widely used to reduce the amount of datarequired to process, transmit, or store a given quantity of information.Data compression is the coding of data to minimize its representation.Compression can be used, for example, to reduce the storage requirementsfor files, to increase the communication rate over a channel, or toreduce redundancy prior to encryption for greater security. However,data compression consumes a significant amount of computing (e.g.central processing unit “CPU”) resources. Also, data can be lost due toproblems such as system crashes, hardware failures, and abnormalcomputing system halts. Journaled file systems can be used to maintaindata integrity when these types of problems occur.

SUMMARY OF THE DESCRIBED EMBODIMENTS

In one embodiment, a method is provided for data decompression using aconstruction area using at least one processor device in a computingenvironment. In one embodiment, by way of example only, for readingcompressed data stored in a journaling format, the method decompressesdata from compressed data blocks and copies the decompressed data intothe construction area in a sequential order to temporarily store thedecompressed data for conducting sequential read operations from theconstruction area.

In another embodiment, a computer system is provided for datadecompression using a construction area using at least one processordevice in a computing environment. The computer system includes acomputer-readable medium and at least one processor in operablecommunication with the computer-readable medium. In one embodiment, byway of example only, read operations, using at least one processordevice decompresses data from compressed data blocks and copies thedecompressed data into the construction area in a sequential order totemporarily store the decompressed data for conducting sequential readoperations from the construction area.

In a further embodiment, a computer program product is provided for datadecompression using a construction area using at least one processordevice in a computing environment. The computer-readable storage mediumhas computer-readable program code portions stored thereon. Thecomputer-readable program code portions include a first executableportion that decompresses data from compressed data blocks and copiesthe decompressed data into the construction area in a sequential orderto temporarily store the decompressed data for conducting sequentialread operations from the construction area.

In addition to the foregoing exemplary method embodiment, otherexemplary system and computer product embodiments are provided andsupply related advantages. The foregoing summary has been provided tointroduce a selection of concepts in a simplified form that are furtherdescribed below in the Detailed Description. This Summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used as an aid in determiningthe scope of the claimed subject matter. The claimed subject matter isnot limited to implementations that solve any or all disadvantages notedin the background.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict embodiments of the invention and are not therefore to beconsidered to be limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a computer storage environmenthaving an exemplary storage device in which aspects of the presentinvention may be realized;

FIG. 2 is a block diagram illustrating a hardware structure of anexemplary data storage system in a computer system in which aspects ofthe present invention may be realized;

FIG. 3 illustrates an exemplary block diagram showing a compressedjournal file system;

FIG. 4 is a flowchart illustrating an exemplary method for datadecompression using a construction area in which aspects of the presentinvention may be realized;

FIG. 5 illustrates an exemplary block diagram showing a sequential readpattern in which aspects of the present invention may be realized;

FIG. 6A-C is a block diagram illustrating a cache divided into aconstruction area and random read cache in which aspects of the presentinvention may be realized;

FIG. 7 is a flowchart illustrating an exemplary alternative method fordata decompression using a construction area in which aspects of thepresent invention may be realized;

FIG. 8 is a flowchart illustrating an exemplary alternative method fordata decompression using a construction area for a read operation inwhich aspects of the present invention may be realized; and

FIG. 9 is a flowchart illustrating an exemplary alternative method fordata decompression using a construction area for a write operation inwhich aspects of the present invention may be realized.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Compressing data is an efficient way to save space on storage systems.It allows enhanced space efficiency by compressing user data to thestorage in real time and decompressing it on user read demand. Improvingrestore speed for backup systems that use inline Chunk-BasedDeduplication is designed to reduce the amount of disk input/output(I/Os) done per each section.

For example, slow restoration due to chunk fragmentation is a seriousproblem facing inline chunk-based data deduplication systems: restorespeeds for the most recent backup can drop orders of magnitude over thelifetime of a system. To improve slow restoration, the following may beperformed: increasing cache size, container capping, and using a forwardassembly area—for alleviating this problem. Container capping is aningest-time operation that reduces chunk fragmentation at the cost offorfeiting some deduplication, while using a forward assembly area is arestore-time caching and prefetching technique that exploits the perfectknowledge of future chunk accesses available when restoring a backup toreduce the amount of RAM required for a given level of caching atrestore time.

For example, a forward assembly area is a restore-time caching andprefetching technique that may use one chunk-container-sized I/O buffer,where a large forward assembly area where the next M bytes of therestored backup will be assembled, and a recipe buffer large enough tohold the part of the recipe that describes the piece being assembled. Inthe simplest case, M-byte slices of the backup are restored at a time byfirst assembling each M-byte backup slice in the forward assembly areaand then sending it out in a single piece. To restore an M-byte slice,the corresponding part of the recipe is first read into the recipebuffer. From that recipe part, it is determined which chunks are neededto fill which byte ranges (chunk spots) of the forward assembly area.

Additionally, in some compressed data systems, data is written to diskin a log-structured (journal) format. Data is compressed in the order itis written by the user/application (time-based-compression/temporallocality). After user data is compressed, it is written into physicalfixed-size blocks, each compressed block might hold several user logsfrom different and not adjacent virtual offsets.

More specifically, in a data processing system or computing environment,a journaling (e.g., a block) storage system may be used to store writeoperations in a journal (e.g., in a block). In a compressed journalsystem, the journal (e.g., block) holds compressed data. Journal systemmaintains file system integrity by recording information regardingupdates to directories, bitmaps, and/or data, in a log, also called ajournal, before the updates are written to a storage device such as ahard disk. In the event of a system crash or other problem, theinformation in the journal may be used to restore the file system to aconsistent state. Full-journaling systems additionally perform datajournaling, in which data updates are also stored in the journal, toensure that no committed data is lost. In one embodiment, the ability toaccess the data randomly is accomplished by dividing the journal intoblocks that use a separate dictionary.

Journal (e.g., block) storage may be characterized by the write patternof the journal/block storage. Data chunks are stored in the order theywere written, so a logical offset of the data chunk has little or norelation to the physical location of the data chunk on the storagebackend. Each data chunk is stored following the previous data chunk andinvalidates any earlier data chunks written to same logical area.

Such approach improves the efficiency when it comes to serving randomand/or read-in-write-order I/O patterns. However, this approach has somedownsides when comes to sequential data read. In a worst case scenariothe following example is provided. A sequential read (in big chunks) ofdata is written with random distribution characteristics. In this case,each user read is likely to require multiple physical blocks to be readand decompressed. Each block is read, decompressed and some of theblock's data is used to serve the user read. However, since user offsetsinside physical blocks are not necessarily adjacent, most of the dataremain unused in cache. Moreover, since cache size is limited, manyblocks will be evicted before further data will be consumed. Thesequential read pattern ensures it will be read and decompressed again,causing I/O and CPU overhead.

To improve the efficiency relating to the above I/O patterns, thepresent invention provides a solution for high performance sequentialuser read from compressed volumes by decompressing data using aconstruction area. In one embodiment, by way of example only, forreading compressed data stored in a journaling format, data fromcompressed data blocks are decompressed. The decompressed data is thencopied into the construction area in a sequential order to temporarilystore the decompressed data for conducting sequential read operationsfrom the construction area. Thus, the present invention provides asolution for usage of log data structure, forward Assembly area, andsequential read pattern detection to form a “construction area”. Theconstruction area cuts down not only the redundant disk reads but alsothe CPU required for the decompression process. In one embodiment, forserving sequential read patterns from a compressed journal storagesystem, the construction area cache algorithm is used to temporarilystore the read and decompressed data in a user view sequential order tominimize disk I/Os and CPU utilization while serving the data to theuser.

In one embodiment, when a sequential read pattern is detected, aconstruction area is allocated in the cache. Each section read by theuser will require extracting data from several blocks on the disk. Sincedata was written with random distribution characteristics, each of theseblocks may consist of logs of data, which will be relevant only forlater on user read sections. These sections will also be required sincethe sequential read pattern will eventually reach them. During thesequential read, each of the extracted data block logs, which are readand decompressed are copied in to the construction area. Each log iscopied into its own designated area in the construction area. The datablock logs are ordered by their user view of the file, i.e. virtualview. Each section in the construction area, already returned to theuser, is freed. Free sections can either be re designated for othercache uses or can be used for cyclic buffer implementation.

Thus, the present invention allows for dramatic reduction of disk I/Osas well as drastic improvement of CPU utilization during sequential readof compressed volumes. Also, the embodiments described herein allow fora reduction in I/Os and improves CPU utilization by using the memorymuch more efficiently then the standard LRU caching.

Thus, the by adapting the in-memory cache into a construction area, theconstruction area allows for achieving a high hit ratio in specificworkloads. Moreover, the construction areal does not require any diskspace allocation or additional I/Os, and the in-memory cache is used forserving both random and sequential patters.

Turning to FIG. 1, an example computer system 10 is depicted in whichaspects of the present invention may be realized. Computer system 10includes central processing unit (CPU) 12, which is connected to massstorage device(s) 14 and memory device 16. Mass storage devices mayinclude hard disk drive (HDD) devices. The operations of the presentinvention further described may be executed on device(s) 14, located insystem 10 or elsewhere. Memory device 16 and mass storage device 14 maybe connected to CPU 12 via a signal-bearing medium or other deviceavailable for connection, attachment, and/or communication used by oneof ordinary skill in the art. In addition, CPU 12 may be connectedthrough communication port 18 (and/or any other device available forconnection, attachment, and/or communication used by one of ordinaryskill in the art) to a communication network 20. Also, additionalcomputer systems 22 and 24 may be directly attached to the CPU 12 and/orindirectly attached to the CPU 12 using the communication network 20and/or the communication port 18 by using any available type of hardwareand/or software device available for connection, attachment, and/orcommunication used by one of ordinary skill in the art. However, theadditional computer systems 22 and 24 may not be necessary. The computersystem 10 may, but are not necessary, include one or more processordevices (e.g., CPU 12) and additional memory devices 16 for eachindividual component of the computer system 10 to execute and performeach operation described herein to accomplish the purposes of thepresent invention. It should be noted that FIG. 1 and/or FIG. 2 areprovided as examples of a variety of types of computing architecturesfor implementing the embodiments of the present invention but should notbe viewed as limited computing architectures. In other words, thepresent invention may use one of a multiplicity of computingarchitectures with a variety of types of computer architectures,computing hardware, processor devices, and software applications forcarrying out the embodiments of the present invention as describedherein.

FIG. 2 is an exemplary block diagram 200 showing a hardware structure ofa data storage system in a computer system according to the presentinvention. Host computers 210, 220, 225, are shown, each acting as acentral processing unit for performing data processing as part of a datastorage system 200. The hosts (physical or virtual devices), 210, 220,and 225 may be one or more new physical devices or logical devices toaccomplish the purposes of the present invention in the data storagesystem 200. In one embodiment, by way of example only, a data storagesystem 200 may be implemented as IBM® System Storage™ DS8000™. A Networkconnection 260 may be a fibre channel fabric, a fibre channel point topoint link, a fibre channel over ethernet fabric or point to point link,a FICON or ESCON I/O interface, any other I/O interface type, a wirelessnetwork, a wired network, a LAN, a WAN, heterogeneous, homogeneous,public (i.e. the Internet), private, or any combination thereof. Thehosts, 210, 220, and 225 may be local or distributed among one or morelocations and may be equipped with any type of fabric (or fabricchannel) (not shown in FIG. 2) or network adapter 260 to the storagecontroller 240, such as Fibre channel, FICON, ESCON, Ethernet, fiberoptic, wireless, or coaxial adapters. Data storage system 200 isaccordingly equipped with a suitable fabric (not shown in FIG. 2) ornetwork adapter 260 to communicate. Data storage system 200 is depictedin FIG. 2 comprising storage controller 240 and storage 230.

To facilitate a clearer understanding of the methods described herein,storage controller 240 is shown in FIG. 2 as a single processing unit,including a microprocessor 242, system memory 243 and nonvolatilestorage (“NVS”) 216, which will be described in more detail below. It isnoted that in some embodiments, storage controller 240 is comprised ofmultiple processing units, each with their own processor complex andsystem memory, and interconnected by a dedicated network within datastorage system 200. Storage 230 may be comprised of one or more storagedevices, such as storage arrays, which are connected to storagecontroller 240 by a storage network.

In some embodiments, the devices included in storage 230 may beconnected in a loop architecture. Storage controller 240 manages storage230 and facilitates the processing of write and read requests intendedfor storage 230. The system memory 243 of storage controller 240 storesthe operation software 250, program instructions and data, which theprocessor 242 may access for executing functions and method stepsassociated with managing storage 230, and executing the steps andmethods of the present invention. As shown in FIG. 2, system memory 243may also include or be in communication with a cache 245 for storage230, also referred to herein as a “cache memory”, for buffering “writedata” and “read data”, which respectively refer to write/read requestsand their associated data. In one embodiment, cache 245 is allocated ina device external to system memory 243, yet remains accessible bymicroprocessor 242 and may serve to provide additional security againstdata loss, in addition to carrying out the operations as describedherein.

In some embodiments, cache 245 is implemented with a volatile memory andnonvolatile memory and coupled to microprocessor 242 via a local bus(not shown in FIG. 2) for enhanced performance of data storage system200. The NVS 216 included in data storage controller is accessible bymicroprocessor 242 and serves to provide additional support foroperations and execution of the present invention as described in otherfigures. The NVS 216, may also referred to as a “persistent” cache, or“cache memory” and is implemented with nonvolatile memory that may ormay not utilize external power to retain data stored therein. The NVSmay be stored in and with the cache 245 for any purposes suited toaccomplish the objectives of the present invention. In some embodiments,a backup power source (not shown in FIG. 2), such as a battery, suppliesNVS 216 with sufficient power to retain the data stored therein in caseof power loss to data storage system 200. In certain embodiments, thecapacity of NVS 216 is less than or equal to the total capacity of cache245.

Storage 230 may be physically comprised of one or more storage devices,such as storage arrays. A storage array is a logical grouping ofindividual storage devices, such as a hard disk. In certain embodiments,storage 230 is comprised of a JBOD (Just a Bunch of Disks) array or aRAID (Redundant Array of Independent Disks) array. A collection ofphysical storage arrays may be further combined to form a rank, whichdissociates the physical storage from the logical configuration. Thestorage space in a rank may be allocated into logical volumes, whichdefine the storage location specified in a write/read request.

In one embodiment, the storage system as shown in FIG. 2 may include alogical volume, or simply “volume,” may have different kinds ofallocations. Storage 230 a, 230 b and 230 n are shown as ranks in datastorage system 200, and are referred to herein as rank 230 a, 230 b and230 n. Ranks may be local to data storage system 200, or may be locatedat a physically remote location. In other words, a local storagecontroller may connect with a remote storage controller and managestorage at the remote location. Rank 230 a is shown configured with twoentire volumes, 234 and 236, as well as one partial volume 232 a. Rank230 b is shown with another partial volume 232 b. Thus volume 232 isallocated across ranks 230 a and 230 b. Rank 230 n is shown as beingfully allocated to volume 238—that is, rank 230 n refers to the entirephysical storage for volume 238. From the above examples, it will beappreciated that a rank may be configured to include one or more partialand/or entire volumes. Volumes and ranks may further be divided intoso-called “tracks,” which represent a fixed block of storage. A track istherefore associated with a given volume and may be given a given rank.

The storage controller 240 may include a construction area module 255, adetection module 257, a data log module 259, and a decompression module261. The construction area module 255, the detection module 257, thedata log module 259, and the decompression module 261 may work inconjunction with each and every component of the storage controller 240,the hosts 210, 220, 225, and storage devices 230. Both the constructionarea module 255, the detection module 257, the data log module 259, andthe decompression module 261 may be structurally one complete module ormay be associated and/or included with other individual modules. Theconstruction area module 255, the detection module 257, the data logmodule 259, and the decompression module 261 may also be located in thecache 245 or other components of the storage controller 240 toaccomplish the purposes of the present invention.

The storage controller 240 includes a control switch 241 for controllingthe fiber channel protocol to the host computers 210, 220, 225, amicroprocessor 242 for controlling all the storage controller 240, anonvolatile control memory 243 for storing a microprogram (operationsoftware) 250 for controlling the operation of storage controller 240,data for control and each table described later, cache 245 fortemporarily storing (buffering) data, and buffers 244 for assisting thecache 245 to read and write data, a control switch 241 for controlling aprotocol to control data transfer to or from the storage devices 230,and construction area module 255, the detection module 257, the data logmodule 259, and the decompression module 261 in which information may beset. Multiple buffers 244 may be implemented with the present inventionas described herein.

In one embodiment, the host computers or one or more physical or virtualdevices, 210, 220, 225 and the storage controller 240 are connectedthrough a network adaptor (this could be a fibre channel) 260 as aninterface i.e., via a switch called “fabric.” In one embodiment, theoperation of the system shown in FIG. 2 will be described. Themicroprocessor 242 may control the memory 243 to store commandinformation from the host device (physical or virtual) 210 andinformation for identifying the host device (physical or virtual) 210.The control switch 241, the buffers 244, the cache 245, the operatingsoftware 250, the microprocessor 242, memory 243, NVS 216, andconstruction area module 255, the detection module 257, the data logmodule 259, and the decompression module 261 are in communication witheach other and may be separate or one individual component(s). Also,several, if not all of the components, such as the operation software245 may be included with the memory 243. Each of the components withinthe devices shown may be linked together and may be in communicationwith each other for purposes suited to the present invention.

FIG. 3 illustrates an exemplary block diagram 300 showing a compressedjournal file system. In a compressed journal system, the journal (e.g.,block) holds compressed data. As illustrated in FIG. 3, the journalingfile system may be used to store the write operations in a journal asshown by W1, W2, W3, W4, and W5 (the block diagram 300 illustrates timeon a Y-axis and user space on an X-axis along with directional areas fororientation purposes). The data is compressed as W1, W2, W3, W4, and W5,which then may be stored in block segments 1, 2, 3, and 4. The journalsystem maintains file system integrity by recording informationregarding updates to directories, bitmaps, and/or data, in a log, alsocalled a journal, before the updates are written to a storage devicesuch as a hard disk. In the event of a system crash or other problem,the information in the journal may be used to restore the file system toa consistent state. Full journaling systems additionally perform datajournaling, in which data updates are also stored in the journal, toensure that no committed data is lost. In one embodiment, the ability toaccess the data randomly is accomplished by dividing the journal intoblocks that use a separate dictionary.

FIG. 4 is a flowchart illustrating an exemplary method 400 for datadecompression using a construction area in which aspects of the presentinvention may be realized. The method 400 begins (step 402) bydecompressing data from compressed data blocks and copies thedecompressed data into the construction area in a sequential order totemporarily store the decompressed data for conducting sequential readoperations from the construction area (step 404). The method 400 ends(step 406).

Turning now to FIG. 5 an exemplary block diagram 500 showing asequential read pattern is illustrated. In one embodiment, the presentinvention uses designated sections of a cache memory for theconstruction area in a compressed volumes storage system, following adetection of sequential read pattern. User space (virtual space) 502should be divided into segments of reasonable size (e.g., 64 megabytesand/or a predefined size, calculated size, and/or a size determinedaccording to the hardware/software capabilities). This allowsdetermining a boundary on the construction area's 508 size. (Forillustration purposes each data block in FIG. 5 is numerically labeledusing the numbers 1-15). It should be noted that the virtual spaceshould be divided into reasonable size segments when the system isconfigured (i.e., before data is written). This way a specific blockcould hold logs relevant to only one of these segments. Blocks of data504 (illustrated in FIG. 5 as 504A-C) are read in the compressed volume506. When sequential read pattern is detected, a region in the cachememory is allocated for a construction area 508.

For handling a user sequential read, the following steps areexecuted. 1) A sequential read is detected and a construction area isallocated. 2) For each user read, all required blocks are read from thedisk/compressed volume (if not already in the cache). It should be notedthat each user read is likely to invoke several disk reads (since datawas written in a random manner), 3) Data from each read block isdecompressed and copied to its designated area in the construction area.4) The construction area stores the decompressed logs until reached byuser sequential read. 5) Along the progress of the user's sequentialread, the construction area already consumed is freed and returned tothe cache's management algorithm. On optimum conditions, theconstruction area should allow to read and/or decompress each blockexactly once thus reducing IO and CPU overhead to minimum possible.

FIG. 6A-C illustrates an exemplary block diagram 600, 650, and 675showing a cached dividing into a construction area and random readcache. As illustrated in FIG. 6, as one embodiment, in order to addressthe sequential read challenge, the entire memory 612 allocated for cachein a system may be divided into several separated areas with portions ofthe cache allocated exclusively for the construction area 608. Othercache regions, for example, such as random read cache 604 and optionread cache 602 may be separated out in the cache memory 612. This cachedivision may, and should, be done dynamically according to the read andwrite patterns in the storage system at each time.

User virtual space shall be divided into segments. Segment's size shouldhave an upper bound according to the cache size such that a significantpart of the segment could be held in the cache's construction area atany time. That is, segment size is advised to be smaller than the sizeof the cache but improved performance can be achieved even if only ahalf or third of the segment can fit into the construction area. Forexample, a segment size is 64 megabytes (MB). This is done to bind thesize of the construction area stripe 606 (illustrated as 606A-D in FIG.6 650) required by each region. The entire area allocated asconstruction area 608 will be divided into stripes 606 of the same size,and each stripe 606 associated with one segment at a time. A stripeheader 610 contains a bitmask describing which chunks are alreadypresent on the stripe 606, and each data chunk is of system's I/Ogranularity size. For example, 16 KB of bitmask data can describe 64 MBsegment when using 512B alignment.

FIG. 7 is a flowchart illustrating an exemplary alternative method 700for data decompression using a construction area in which aspects of thepresent invention may be realized. The method 700 begins (step 702) bydividing a cache into a construction area and a random cache (step 704).The method 700 allocates the construction area in designated areas ofthe cache (step 706). The method 700 determines a boundary size of theconstruction area (step 708). The method 700 divides the constructionarea into multiple stripes (step 710). Each stripe is associated withone similar size segment of virtual space at a time. Also, theconstruction area in each volume may be divided in half if a requiredsize of the construction area exceeds a total cache size. The method 700extracts the data from different data sections of compressed data blocksfor the decompressing (step 712). The method 700 copies data logs fromeach of the extracted data sections of the compressed data blocks intothe construction area (step 714). The method 700 orders the copied datalog(s) in a virtual view (step 716). The method 700 ends (step 718).

FIG. 8 is a flowchart illustrating an exemplary alternative method 800for data decompression using a construction area for a read operation inwhich aspects of the present invention may be realized. The method 800begins (step 802) by, for each region of the read operation, determiningwhether each of the regions of the read operation is in a constructionarea and/or a random cache (step 804). Each region, which is determinedto be included in either the construction area and/or the random cache,is served to the user (step 814). For each region, which is determinednot to be included in either the construction area and/or in the randomcache, all of the compressed data blocks containing its data (e.g.,containing the data logs of each of the regions) are read (step 806).All of the compressed data blocks containing the region's data (e.g.,data logs of each of the regions) are decompressed (step 808). Each ofthe compressed data blocks is copied into one of the stripes in theconstruction area (step 810), and the stripes header in the constructionarea is updated and the copied data logs are marked as present (e.g.,present/existing in the construction area) (step 812). The method 800ends (step 816).

As illustrated in FIG. 8, the presence of each region that is readshould be checked in both the random read cache and the constructionarea prior to an input/output (I/O) and a decompression task. In case aregion is present in one of these structures, that particular region maybe served directly from there. For a region missing in both caches: 1)all blocks containing the required region's parts are read, 2) adecompression task is performed for each block, and 3) the uncompresseddata is copied to the adequate stripe in the Construction Area. Updatethe stripe's header according to the copied logs.

It should be noted that write operations will invalidate regions in thecache. For areas present in the construction area there are twoalternatives. First, when a region is invalidated, an additional I/O anda decompression task are executed to restore the invalided region intothe construction area when a sequential user read reaches theinvalidated area. Second, upon a write acknowledgement from the disk,the invalidated region is updated with newly written user data andremains in construction area with new data. This is illustrated below inFIG. 9.

FIG. 9 is a flowchart illustrating an exemplary alternative method 900for data decompression using a construction area for a write operationin which aspects of the present invention may be realized. The method900 begins (step 902) by determining if the write operation invalidatesany regions in the cache (step 904). If no, the method 900 ends (step912). If yes, the method 900 determines which cache update method (e.g.,updated a region and/or invalidate a region) is to be used (step 906).The method 900 may select one of two options by 1) marking a region inthe cache as invalid, and re-reading and decompressing the region upon auser read demand (step 908), and/or 2) upon a write acknowledgement fromthe disk, updating the invalidated cache region with newly written userdata and remains in construction area with new data (step 910). Themethod 900 ends (step 912). More specifically, at step 906, the regionis invalidated, causing an additional I/O and a decompression task torestore the in region into the construction area when sequential userread reaches the invalidated region.

In a further embodiment, in order to enhance the advantages of using theconstruction area during user sequential read and reduce the lay back ofthe user sequential read during random I/O, the present inventionprovides for dynamic allocation of cache sections. Using a decisionalgorithm, the cache will be divided to two sections, a constructionarea cache and random cache by the following heuristics. When nosequential read is performed, all cache memory is used as the randomcache. The construction area is always preferred over the random cache.Performance improvement using a construction area during sequential readpattern is much more significant then the one gained from using randomcache in random I/O pattern. In case a required construction areaexceeds cache memory each volumes construction area will be cut in tohalf. For example, two volumes now with the half segment sizeconstruction area cache enhance system performance as compared to onevolume with the whole segment size construction area and another usingno cache at all. The sequential read using the construction area halfthe size of a segment will cause up to two reads of each data block (inthe worst case scenario).

The construction area improves the sequential read patterns fromcompressed volumes dramatically. The construction area allows not only areduction of disk I/O's, but also reduces the CPU utilization. Theconstruction area is most efficient when used in systems in which theuser space is divided into segments. In these systems the upper boundfor the construction area's size is merely the size of a single segment.The construction area allows efficient sequential read of multiplevolumes being read at the same time. In addition, the construction areasupports efficient sequential read during on going writes to the readvolumes. The construction area also provides for increased computingefficiency for randomly accessed volumes while other volumes are beingsequentially read.

In the worst case scenario, the sequential read of user segment writecause the following: the read blocks (I/O) equal the logs in segment,the decompressed blocks equal the logs in segment. Using a ConstructionArea, the read blocks (I/O) now equal the blocks in segment, and thedecompressed blocks now equal the blocks in segment. Each compressedblock may hold multiple user logs, depending on the user write size andthe compression ration achieved for this data. Thus, the predictedperformance improvement using the proposed solution is substantial. Forexample, consider the following scenario with a system with a cache sizeequal to 4 GB, a block size equal to 32 KB, a segment size equal to 64MB (e.g., approximately 700 blocks with 65% compression ratio), activesegments equal to 1024, segments being sequentially read equal to 10%,and logs per block equal to/or approximately 20. In this example, theuser is reading data in block size (32 KB) chunks.

Using all cache as random cache (LRU), each segment will useapproximately 128 cache blocks of size 32 KB. In the worst-case scenariocache hits rate will be approximately 0%. Thus, for each segment thenumber of blocks read and decompressed is approximately equal to thenumber of logs read which is approximately equal to the block in segmentmultiplied by 20.

Using a Construction Area, for each one of the approximately 100segments being sequentially read a construction area of sizeapproximately 40 MB will be allocated. The cache hit rate for thesegments being sequentially read will be greater than and/or equal to62%. The cache hit rate for the rest of the segments will beapproximately 0%. For each sequentially read segment the number ofblocks read and decompressed approximately equal to blocks in segmentmultiplied by 1.6

Thus, in comparison between the construction area versus the LRU cache,for the random accessed segments there is no significant difference. Forthe sequentially read segments the number of blocks read anddecompressed using a construction area is cut to approximately 8%.

In one embodiment, the present invention provides for data decompressionusing a construction area using at least one processor device in acomputing environment. In one embodiment, by way of example only, forreading compressed data stored in a journaling format, the methoddecompresses data from compressed data blocks and copies thedecompressed data into the construction area in a sequential order totemporarily store the decompressed data for conducting sequential readoperations from the construction area.

In one embodiment, the present invention detects sequential readpatterns from the plurality of compressed data blocks.

In one embodiment, the present invention performs at least one of:dividing a cache into a construction area and a random cache, whereinthe random cache is when there are no sequential read operations and theconstruction area is used for sequential read operations, allocating theconstruction area in designated areas of the cache, extracting the datafrom different data sections of the plurality of compressed data blocksfor the decompressing, copying data logs from each of the extracted datasections of the plurality of compressed data blocks into theconstruction area, and/or ordering the copied data logs in a virtualview.

In one embodiment, the present invention performs each one of: freeingeach section of the construction area, and redesignating the freesections of the construction area for one of a plurality of cache usesand cyclic buffer implementation.

In one embodiment, the present invention performs at least one of:dividing virtual space into similar size segments, determining aboundary size of the construction area, dividing the construction areainto a plurality of stripes, wherein each of the plurality of stripes isassociated with one of the similar size segments of virtual space at atime, and/or including dividing the construction area of each one of aplurality of volumes in half if a required size of the construction areaexceeds a total cache size.

In one embodiment, the present invention performs, for a read operation,performing at least one of: determining whether one of a plurality ofregions of the read operation is in one of a construction area and arandom cache, if the one of the plurality of regions is determined to beincluded in one of the construction area and the random cache:extracting one of the plurality of regions of the read operation, and ifthe one of the plurality of regions is determined not to be included inone of the construction area and the random cache: reading all of theplurality of compressed data blocks containing each one of the pluralityof regions, decompressing all of the plurality of compressed data blockscontaining each one of the plurality of regions, copying all of theplurality of compressed data blocks containing each one of the pluralityof regions into one of the plurality of stripes in the constructionarea, and updating a header of one of the plurality of stripes accordingto copied data logs.

In one embodiment, the present invention performs, for a writeoperation, restoring to the construction area an invalidated regioncaused by the write operation by the decompressing.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunchcards or raised structures in a groove having instructions recordedthereon, and any suitable combination of the foregoing. A computerreadable storage medium, as used herein, is not to be construed as beingtransitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method for data decompression using aconstruction area by a processor device in a computing environment, themethod comprising: for reading compressed data stored in a journalingformat, decompressing data from a plurality of compressed data blocksand copying the decompressed data into the construction area in asequential order to temporarily store the decompressed data forconducting sequential read operations from the construction area.
 2. Themethod of claim 1, further including dividing a cache into aconstruction area and a random cache, wherein all of the cache is usedas the random cache when there are none of the sequential readoperations and the construction area is allocated and used for thesequential read operations.
 3. The method of claim 2, further includingperforming at least one of: allocating the construction area indesignated areas of the cache, extracting the data from different datasections of the plurality of compressed data blocks for thedecompressing, copying data logs from each of the extracted datasections of the plurality of compressed data blocks into theconstruction area, and ordering the copied data logs in a virtual view.4. The method of claim 1, further including performing at least one of:freeing each section of the construction area, and redesignating thefree sections of the construction area for one of a plurality of cacheuses and cyclic buffer implementation.
 5. The method of claim 1, furtherincluding performing at least one of: dividing virtual space intosimilar size segments, determining a boundary size of the constructionarea, dividing the construction area into a plurality of stripes,wherein each of the plurality of stripes is associated with one of thesimilar size segments of virtual space at a time, and including dividingthe construction area of each one of a plurality of volumes in half if arequired size of the construction area exceeds a total cache size
 6. Themethod of claim 1, further including, for a read operation, performingat least one of: determining whether one of a plurality of regions ofthe read operation is in one of a construction area and a random cache,if the one of the plurality of regions is determined to be included inone of the construction area and the random cache: extracting one of theplurality of regions of the read operation, and if the one of theplurality of regions is determined not to be included in one of theconstruction area and the random cache: reading all of the plurality ofcompressed data blocks containing each one of the plurality of regions,decompressing all of the plurality of compressed data blocks containingeach one of the plurality of regions, copying all of the plurality ofcompressed data blocks containing each one of the plurality of regionsinto one of the plurality of stripes in the construction area, andupdating a header of one of the plurality of stripes according to copieddata logs.
 7. The method of claim 1, further including, for a writeoperation, performing at least one of: invalidating a matching area inthe construction area thereby causing the matching area to be re-readand decompressed, and updating a location of the construction area withnewly written data upon receiving an acknowledgement from a storagesystem.
 8. A system data decompression using a construction area in acomputing environment, comprising: at least one processor device,operable in the computing storage environment, wherein the processordevice: for reading compressed data stored in a journaling format,decompresses data from a plurality of compressed data blocks and copyingthe decompressed data into the construction area in a sequential orderto temporarily store the decompressed data for conducting sequentialread operations from the construction area.
 9. The system of claim 8,wherein at least one processor device divides a cache into aconstruction area and a random cache, wherein all of the cache is usedas the random cache when there are none of the sequential readoperations and the construction area is allocated and used for thesequential read operations.
 10. The system of claim 9, wherein the atleast one processor device performs at least one of: allocating theconstruction area in designated areas of the cache, extracting the datafrom different data sections of the plurality of compressed data blocksfor the decompressing, copying data logs from each of the extracted datasections of the plurality of compressed data blocks into theconstruction area, and ordering the copied data logs in a virtual view.11. The system of claim 8, wherein the at least one processor deviceperforms at least one of: freeing each section of the construction area,and redesignating the free sections of the construction area for one ofa plurality of cache uses and cyclic buffer implementation.
 12. Thesystem of claim 8, wherein the at least one processor device performs atleast one of: dividing virtual space into similar size segments,determining a boundary size of the construction area, dividing theconstruction area into a plurality of stripes, wherein each of theplurality of stripes is associated with one of the similar size segmentsof virtual space at a time, and including dividing the construction areaof each one of a plurality of volumes in half if a required size of theconstruction area exceeds a total cache size
 13. The system of claim 8,wherein the at least one processor device, for a read operation,performs at least one of: determining whether one of a plurality ofregions of the read operation is in one of a construction area and arandom cache, if the one of the plurality of regions is determined to beincluded in one of the construction area and the random cache:extracting one of the plurality of regions of the read operation, and ifthe one of the plurality of regions is determined not to be included inone of the construction area and the random cache: reading all of theplurality of compressed data blocks containing each one of the pluralityof regions, decompressing all of the plurality of compressed data blockscontaining each one of the plurality of regions, copying all of theplurality of compressed data blocks containing each one of the pluralityof regions into one of the plurality of stripes in the constructionarea, and updating a header of one of the plurality of stripes accordingto copied data logs.
 14. The system of claim 8, wherein the at least oneprocessor device, for a write operation, performs at least one of:invalidating a matching area in the construction area thereby causingthe matching area to be re-read and decompressed, and updating alocation of the construction area with newly written data upon receivingan acknowledgement from a storage system.
 15. A computer program productfor data decompression using a construction area in a computingenvironment by a processor device, the computer program productcomprising a non-transitory computer-readable storage medium havingcomputer-readable program code portions stored therein, thecomputer-readable program code portions comprising: a first executableportion that, for reading compressed data stored in a journaling format,decompresses data from a plurality of compressed data blocks and copyingthe decompressed data into the construction area in a sequential orderto temporarily store the decompressed data for conducting sequentialread operations from the construction area.
 16. The computer programproduct of claim 15, further including a second executable portion thatperforms at least one of: dividing a cache into a construction area anda random cache, wherein all of the cache is used as the random cachewhen there are none of the sequential read operations and theconstruction area is allocated and used for the sequential readoperations, allocating the construction area in designated areas of thecache, extracting the data from different data sections of the pluralityof compressed data blocks for the decompressing, copying data logs fromeach of the extracted data sections of the plurality of compressed datablocks into the construction area, and ordering the copied data logs ina virtual view.
 17. The computer program product of claim 15, furtherincluding a second executable portion that performs at least one of:freeing each section of the construction area, and redesignating thefree sections of the construction area for one of a plurality of cacheuses and cyclic buffer implementation.
 18. The computer program productof claim 15, further including a second executable portion that performsat least one of: dividing virtual space into similar size segments,determining a boundary size of the construction area, dividing theconstruction area into a plurality of stripes, wherein each of theplurality of stripes is associated with one of the similar size segmentsof virtual space at a time, and including dividing the construction areaof each one of a plurality of volumes in half if a required size of theconstruction area exceeds a total cache size
 19. The computer programproduct of claim 15, further including a second executable portion that,for a read operation, performs at least one of: determining whether oneof a plurality of regions of the read operation is in one of aconstruction area and a random cache, if the one of the plurality ofregions is determined to be included in one of the construction area andthe random cache: extracting one of the plurality of regions of the readoperation, and if the one of the plurality of regions is determined notto be included in one of the construction area and the random cache:reading all of the plurality of compressed data blocks containing eachone of the plurality of regions, decompressing all of the plurality ofcompressed data blocks containing each one of the plurality of regions,copying all of the plurality of compressed data blocks containing eachone of the plurality of regions into one of the plurality of stripes inthe construction area, and updating a header of one of the plurality ofstripes according to copied data logs.
 20. The computer program productof claim 15, further including a second executable portion that, for awrite operation, performs at least one of: invalidating a matching areain the construction area thereby causing the matching area to be re-readand decompressed, and updating a location of the construction area withnewly written data upon receiving an acknowledgement from a storagesystem.